Converting between two sets of constants [duplicate]

Question

I have two enums NAME and ALIAS which are guaranteed to have the same number of constants, and I need a way to convert each constant from NAME to its corresponding one from ALIAS, and vice-versa. For example:

def name_to_alias(name):
    if name == Name.PAUL:
        return Alias.STARCHILD
    elif name == Name.GENE:
        return Alias.DEMON
    ...

def alias_to_name(alias):
    if alias == Alias.STARCHILD:
        return Name.PAUL
    elif alias == Alias.DEMON:
        return Name.GENE
    ...

I don't wish to maintain two functions (or dicts) like these. Ideally, I'd have the enum mappings in a single data structure which I can access from both conversion functions.

I'm thinking of something like:

mappings = {
    Name.PAUL: Alias.STARCHILD
    Name.GENE: Alias.DEMON
    ...
}

This would work for converting from Name to Alias, but the opposite may have issues (what happens if I make a copy-paste error and end up with two dict keys with the same value?). Is there an easy and safe way to achieve this?

@Martin That's surprising given you just guaranteed the two enum types have the exact same number of members - how did you compile Alias with colliding member names? Perhaps the mapping isn't as symmetric as you initially suggested? — Mathias R. Jessen
– Mathias R. Jessen, Commented Jul 1, 2024 at 15:51
Your editor (or ultimately the python runtime executing your code) will tell you there's a collision and you can then go back and fix your mistake. I'm afraid I don't understand what sloppy copy-pasting has to do with your question about mapping enum values. Can you tell us more about the relationship between Name and Alias? Is it 1-to-1, or many-to-1? — Mathias R. Jessen
– Mathias R. Jessen, Commented Jul 1, 2024 at 16:01
I guess that your function to get_name from alias should return all matching names, like def alias_to_name(alias): return [name for name, a in mappings.items() if a == alias] — Pepe N O
– Pepe N O, Commented Jul 1, 2024 at 16:04
@Martin I thought you were talking about making a reverse dictionary that would let you look up keys based on their values. — Mark Ransom
– Mark Ransom, Commented Jul 1, 2024 at 16:44

Pepe N O · Accepted Answer · 2024-07-01 16:25:28Z

1

Considering that could occur that in mappings more than one name could have the same alias a safe function should raise an error, like

mappings = {
    Name.PAUL: Alias.STARCHILD,
    Name.GENE: Alias.DEMON,
    Name.PETER: Alias.CATMAN,
    Name.ALICE: Alias.DEMON
}

def alias_to_name(alias):
#check if the alias is more than once in the mappings and raise an error
    if list(mappings.values()).count(alias) > 1:
        raise ValueError('Alias is not unique', alias, [name for name, a in mappings.items() if a == alias])
    else:
        return [name for name, a in mappings.items() if a == alias]

That will output

('Alias is not unique', <Alias.DEMON: 2>, [<Name.GENE: 2>, <Name.ALICE: 4>])

answered Jul 1, 2024 at 16:25

Pepe N O

2,3841 gold badge12 silver badges17 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Martin Over a year ago

Yes, that's what I was thinking. But I was expecting that a more "elegant" solution would exist, e.g. use a different data structure entirely, etc.

Mark Ransom Over a year ago

That's a linear search. Might be fine for short lists, but very costly for large ones. Not only that but the check for multiple aliases doubles the amount of work required.

Collectives™ on Stack Overflow

Converting between two sets of constants [duplicate]

1 Answer 1

2 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Linked

Related